Treadmills are presently utilized as advantageous means for performing vigorous exercise indoors and at a stationary position. Such treadmills are typically comprised of an elongated closed-loop belt supported by a plurality of rotatable rollers arranged at closely-spaced parallel intervals and being mounted in a freewheeling manner. In order to limit the linear speed of the belt, it is typical to provide a flywheel. The user holds on to the treadmill rail to control speed. Only one known treadmill employs a governor which is both complicated and expensive. It is, therefore, desirable to provide a governor for treadmills and the like which is simple to use and having a simplified and yet rugged and reliable design to enable rapid adjustment of the treadmill linear speed.